Infrared emitting tow target



April 16, 1963 R. J. HOPPER ET AL INFRARED EMITTING Tow TARGET Filed Oct. 22, 1956 2 Sheets-Sheet 2 R. J. HOPPER ET AL INFRARED EMITTING TOW TARGET April 16, 1963 Filed Oct. 22, 1956 3,086,202 INFRARED EMlTllNG TOW TARGET Robert il. Hopper, deceased, late of Pacific Palisades,

Caiif., by .lune Wesley Hopper, exeeutrix, Pacific Palisades, Calif., and Boyd E. Elder, Los Angeles, Calif.,

assignors to Del Mar Engineering Laboratories, Los

Angeles, Calif., a corporation of California Filed Get. 22, 1956,'Ser. No. 617,450 2 Claims. (Cl. 343-18) r[his invention relates to an aerial tow target for practice in the use of devices sensitive to infra-red energy radiations for detecting and/or tracking aerial targets. The invention has special utility for providing realistic eX- perience for lighter pilots, interceptor pilots and various other personnel in the use of various automatic equipment for such purposes -as lire control, missile launching control, and target interception.

Most airborne military vehicles used for offense, such as aircraft `and missiles, have power means that emit infra-red radiations, such power means including not only conventional piston-type internal combustion engines, but also and especially jet engines, turbo-prop engines and rockets. Since such devices for oense by an enemy travel at relatively high speeds, there is need for training practice with high speed targets that emit infra-red radiations. Since self-powered robot targets are too expensive to be expendable on a large scale, there is a further need for a relatively inexpensive infra-red radiating tow target.

The problem arises of how to provide a target suitable for this purpose that will emit sufficient infrared energy to be effective for target :detection and to simulate effectively an actual enemy airborne vehicle. Itis not feasible to use the tow cable for electrically energizing the infrared emitting means on the tow target from a power source on the aircraft since a very long t-ow cable is mandatory to minimize the hazard to the towing aircraft. Such a tow cable may be four or ve miles long or longer, and commonly comprises a wire of relatively small diameter. it is not feasible, moreover, to use battery means on the target itself for generating the infra-red radiations, not only because a battery means is relatively heavy, but also because a relatively large amount of infra-red energy is required. The present invention meets this problem by equipping the tow target with an infra-red generator actuated by energy derived from the air stream. The actuation means for this purpose may be an air turbine or may be a propeller having blades extending radially into the air stream.

It is contemplated that the aerial tow target will have a streamlined configuration suitable for flight through the air at a relatively high air speed. For this purpose, the target may have a slender, tapered, elongated nose probe at its leading end for connection to the tow cable. It is further contemplated that the body of the aerial target may be provided with airfoils to cause the target body to rotate on its longitudinal axis for increased flight stability, such rotation being permitted by -a swivel connection with the tow cable. 1n one practice of the invention, the nose probe is rotatable relative to the target body and serves as the hub of a propeller means for energizing the infrared generator. In another practice of the invention, the nose probe is xed relative to the target body 4and `the propeller means is rotatably mounted on the nose probe.

The preferred practice of the invention is characterized by the use of an infra-red lamp to radiate the infrared energy. It has been found that such a lamp mounted on the tail end of the aerial target effectively simulates the hot gaseous stream discharged by a jet engine or by a rocket-propelling means. In this regard, a feature of the preferred practice of the invention is the enclosure of a high wattage infra-red energy emitting lamp in a protective shell of material transparent to infra-red rays, with provision for the circulation through the shell of cooling air taken from the air stream.

The features and advantages of the invention may be readily understood from the following detailed description considered with the `accompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

FGURE l is a side elevation vof a selected embodiment of the tow target, with portions broken away;

FIGURE 2 is a view partly in side elevation and partly in section, showing the construction of the rotary nose probe;

FIGURE 3 is a view partly in section and partly in side elevation, showing the structure for enclosing the infrared lamp on the tail end of the tow target; and

FIGURE 4 is a sectional view of the leading end of the second form -of a tow target which has a fixed nose or probe member.

The rst embodiment of the invention, shown in FIG- URES l, 2 and 3, comprises a tow target having a relatively light, streamlined body, generally designated 10, having tail tins 12. The tow target body 10, for example, may comprise -a shell 14 of molded plastic or paper provided with suitable internal reinforcement means. Other materials, including foamed cellular plastic, may be used, if desired, to form the body 10. The tail ns 12 may be made of foamed cellular plastic bonded to the body 10 by suitable adhesive. Preferably, -tip portions 15 of the tail fins 12 are bent to angles to cause the tow target body 10 to rotate about its longitudinal aXis in reaction to the air stream, the purpose of such rotation being to stabilize the tow target in flight.

Since it is desirable that a target be radar-reflective and since the tow target body 10 is usually fabricated from' material that does not reflect radar radiations, the tow target body may be equipped with suitable r-adar reflective means. Either monostatic or bistatic radar reflective means may be used. In this instance, the tow target body 10 houses a relatively large monostatic rad-ar corner reflector unit that is generally designated by the numeral 16. The reector unit 16 includes a transverse metal foil reflector surface 18 sandwiched into a lthick transverse wall 20 of foamed cellular plastic. A second metal foil rellector surface 22 in -a central longitudinal plane is sandwiched into a thick diskshaped longitudinal wall 24 of foamed cellular plastic; `and a third metal foil reflector surf-ace 25 is sandwiched into a disk-shaped longitudinal wall 26 in a plane perpendicular to the second metal foil reflector 22. Thus, the three metal foil reflectors are in three planes perpendicular to each other, with all three of the planes intersecting in the middle of the reflector unit.

The means for emitting the infra-red radiations may comprise a conventional infra-red lamp bulb 30 mounted in the trailing end of the tow target body 10, the lamp bulb vbeing oriented for rearward radiation. The lamp bulb 30 may have a rating of 750 to 1,000 watts, for example, and, preferably, is internally silvered to provide a conical reflector 32.

Preferably, the infra-red energy emitting lamp bulb 30 is enclosed by a protective housing having a rear wall of material transparent to infra-red radiations, and a feature of the invention is the further concept of cooling the interior of such a housing, as heretofore mentioned. For example, as best shown in FIGURE 3, the housing for the infra-red lamp bulb 30 may comprise a thin-walled cylindrical extension 34 of the tail portion of the tow target body 10, together With a hernispherical shell 35 of transparent plastic material.

For the purpose of circulating cooling air through the lamp housing, the cylindrical extension 14 may be formed with forwardly directed inlet ports 36 into which air is rammed by the yforward flight of the target. The cylindrical extension 34 may be made of light sheet metal and the sheet metal may be lanced and offset to form the inlet ports 36. The cooling air forced into the lamp housing in this manner may be discharged through a central discharge port 38 in the transparent shell 35.

The infra-red emitting lamp 3) -may be energized by an A.C. generator 40 that is actuated by a propeller means that is generally designated by the numeral 42. Preferably, the generator 40 is a three phase generator and is connected to a suitable three-phase rectifier 44, the rectifier being connected to the infra-red lamp by means of a cable 45.

In this first embodiment of the invention, the propeller means 42 comprises a plurality of radial propeller blades 46 mounted on a slender, elongated, tapered nose probe Si? that is rotatably connected to the tow target body 10 and extends forward therefrom for connection to a tow cable 52. In the construction shown, a suitable swivel joint means is provided on the leading end of the nose probe Sil for connection to the tow cable 52 whereby the nose probe may rotate without interference by the tow cable. For this purpose, a suitable clevis member 54 designed for direct connection to the tow cable 52 is rotatably mounted in a sleeve 55 at the leading end of the nose member 50.

The tapered nose probe 50 may comprise a thin-walled aluminum shell mounted on the forward end of a drive shaft 56, the rear end of the drive shaft -being splined into a coupling collar S of the A.C. generator 40. As best shown in FIGURE 2, the nose member 50 may be fixedly attached by suitable screws 69 to a radial flange 62 on the forward end of the drive shaft 56.

The drive shaft S6 may be journalled by a lforward thrust bearing 64 in a forward internal reinforcement ring 65 of the tow target body structure and may be journalled by a second thrust bearing 66 in a reinforcement bulkhead 68 of the body structure. In the construction shown, the second thrust bearing is in a housing 70 on the rear face of the bulkhead 68 and is connected by screws 72 to a reinforcement ring 74 on the forward face of the bulkhead. For further reinforcement, suitable rigid frame members 75 may connec-t the forward reinforcement ring 65 with the rearward reinforcement ring 74. Thus, the stresses involved in the towing of the target structure by the tow cable 52 are distributed from the nose probe 50 to the body shell 14, both by the forward thrust bearing 64 in cooperation with the reinforcement ring 65, and by the rearward thrust bearing 66 in co-operation with the bulkhead 68.

Preferably, the propeller blades 46 are rotatably mounted on the nose probe 5t) for change in pitch, when desired. In this regard, a further feature of the invention is the provisionl of automatic pitch control means to keep the rotation of the propeller means down to a predetermined constant speed, say a speed of 12,000 r.p.m. For this purpose, a centrifugally-actuated pitch control mechanism of a well known construction may be mounted inside the nose probe 54B, as indicated by the broken line rectangle 76 in FIGURE 2, the pitch control mechanism rotating with the nose probe and being operatively connected to the propeller -blades 46.

The manner in which the first embodiment of the invention serves its purpose may be readily understood from the foregoing description. When the target is towed through the air at high speed by attachment of the tow cable 52 to a suitable tow aircraft, the streamlined target body is free to rotate on its longitudinal axis by the reaction of the angular tip portions of the tail fins 12 thereby increasing the stability of the tow target. The rotation of the target body 10 causes corresponding rotation of the radar corner reflector unit 16 to facilitate radar detection and tracking of the target, when desired. The manner in which the rotation of the target body facilitates radar detection and tracking of the target may be understood when it is considered that the ratio of the intensity of a reflected radar signal from a corner reflector relative to the intensity of the incident radar signal varies with the direction of the incident signal relative to the corner reflector. Thus, with a radar signal of a given intensity directed to the tow target from a given source at a given location, the intensity of the reflected signal will depend upon the attitude or orientation of the radar reflector and rotation of the corner reflector greatly increases the probability that the corner reflector will momentarily assume a position to reflect back to the source a radar wave of relatively high intensity. Since the propeller means comprising the blade-equipped nose probe 50 is rotatably connected to the tow cable 52., as well as rotatably mounted on the target body 10, the propeller means is free to rotate in reaction to the air stream for actuation of the generator 40.

By virtue of the automatic pitch control mechanism 76, the propeller means rotates at a substantially constant speed regardless of the speed of flight and regardless of air flow conditions. As a result, a substantially constant electrical energy output is delivered to the infra-red emitting lamp bulb 30 through the rectifier 44. In this manner, the infra-red lamp St) is continuously energized for continuous infra-red radiation. Any infra-red detecting, tracking, or homing device may be caused to respond to the infra-red radiations from the tow target, and, simultaneously, other detecting or tracking devices employing radar may be made responsive to the radar corner reflector unit 16.

A feature of the described tow target construction is that the rotary nose probe 50 is a relatively rigid member of high structural strength and is capable of supporting the tow target in cooperation with a suitable launcher. Thus, a tow target launching device indicated in broken lines and designated L in FIGURE l may be mounted on a tow airplane in the air stream of the airplane in a well known manner, and the nose probe 50l of the tow target may be releasably telescoped into the launcher for transportation to a point for the start of a target run. This capability of the nose probe 50 for cantilever support of the tow target body is made possible by the rigid attachment of the nose probe to the drive shaft 56 and by the manner in which the drive shaft is journalled in the reinforcement structure of the tow target body.

An important advantage of the relatively great length of the nose probe S0 is that it protects the propeller blades 46 against damage whenever the tow target tends to overshoot when it is reeled into the launcher L. Otherwise the rapidly rotated blades would strike the launcher.

The second embodiment of the invention, the construction of which is indicated by FIGURE 4, is largely identical to the first embodiment, the difference beingT in the construction of the nose probe and the propellerdriven mechanism for actuating the Igenerator. The tow target body 10a has the usual thin-walled shell 14a, which, in this instance, is internally reinforced by a bulkhead '7f3` and a forward internal reinforcement ring 80.

In this embodiment of the invention, the nose probe 50a is rigidly integral with the body 10a, and the propeller means 42a is rotatably mounted on the nose probe. The structure of the nose probe 50a may comprise a rigid axial tube `82, a special collar member S4 on the tube for mounting the propeller means, and an elognated, tapered nose probe shell 85.

The axial tube 82 may be a thin-walled aluminum tube with a reinforcement core 86 of foamed cellular plastic and with a plug insert S8 at its base end. The base end of the aXi-al tube '82 extends through a reinforcement disk 90 on the forward face of the bulkhead 78 and is anchored thereto by suitable `screws 92. The axial tube 82 is embraced and reinforced by the forward reinforcement ring 80 and tapers at its forward end to the usual swivel joint comprising a clevis member 54a rotatably mounted in a sleeve 55a. The tapered nose probe shell 85 which is reinforced by a pair of tapered inner rings 94 is connected at its base end to a circumferential flange 95 of the special collar 84, and at its forward end merges with the axial tube 82.

The propeller means 42a comprises a series of propel- 1er blades 46a iixedly mounted on a hub 96. The hub 96 is rotatably mounted on the special collar 84 by suitable bearings 98 and 100. In the construction shown, the forward end of the body shell 14a carries a iiared reinforcement sleeve 102 that not only cooperates with the inner reinforcement ring 80, but also overhangs the hub 96.

The hub 96 is formed with an inner ring gear 104 that meshes with a pinion 105 on the forward end of a drive shaft 106. The drive shaft 106 is journalled in a bearing |108 in the forward reinforcement ring 80 and in a second bearing 110 in the reinforcement disk 90. A pinion 112 on the rear end of the drive shaft 106, meshes with a gear 114 on the actuating shaft 115 of an A.C. generator 40a. The generator 40a has a flanged base ring 116 enclosing the pinion '112 and the gear 114, this flanged base ring being anchored to the bull;- head 78 by suitable bolts 11S.

Our description in specific detail of selected embodiments of the invention will suggest Various changes, substitutions and other departures from our disclosure within the spirit and scope of the appended claims.

We claim:

1. An aerial tow target comprising a hollow, thinwalled, rigid body member having a low drag aerodynamic configuration, a forward end, a trailing end, and a longitrudinal axis, the walls of said body member being formed of a non-metallic material permeable by radar waves; means defining a plurality of normally intersecting planes attached to said body member and positioned interiorly of said body member and having a metallic surface for reecting exteriorly propagated radar waves; aerodynamic means carried on said body member for continuously rotating said body member about its longitudinal axis to stabilize said body member in flight whereby said plurality of intersecting planes are rotated with said body member to increase the probability of detection of the tow target by the reflected radar waves; an infrared emitter carried by said body member at the trailing end of said body member to simulate the infrared radiations from the power plant of a self-propelled aerial vehicle; a generator carried by said body member interiorly of said body member and connected to energize said infrared emitter; propeller means rotatable about the longitudinal axis of said body member and being carried by said body member at the forward end of said body member for continuous rotation with respect to -said body member as said body member is moved through the air, and means operatively connecting said propeller means to said generator for actuation of the generator by the propeller means whereby the generator energizes said infrared emitter.

2. An aerial tow target comprising a hollow, thinwalled, rigid body member having a low drag aerodynamic configuration, a forward end, a trailing end and a longitudinal axis, aerodynamic means carried by said body member for continuously rotating said body member about its longitudinal axis to stabilize said body member in flight, an infrared emitter carried by said body member at the trailing end of said body member to simulate the infrared radiations from the power plant of a selfpropelled aerial vehicle; a generator carried by `said body member interiorly of said body member and connected to energize said infrared emitter; and propeller means rotatable about the longitudinal axis of said body member and being carried by said body member at the forward end of said body member for continuous rotation with respect to said body member as said body member is moved through the air, and means operatively connecting said propeller means to said generator for actuation of the generator by the propeller means whereby the generator energizes said infrared emitter.

References Cited in the file of this patent UNITED STATES PATENTS 1,893,149 Picco Ian. 3, 1933 1,893,287 Jenkins Jan. 3, 19313 2,122,766 Wiemer July 5, 1938 2,243,618 Brown May 27, 1941 2,342,651 Dircksen Feb. 29, 1944 2,381,130 Lloyd Aug. 7, 1945 2,419,549 Griesinger Apr. 29, 1947 2,463,517 Chromak Mar. 8, 1949 2,550,229 Cotton Apr. 24, 1951 2,583,369 Fumagalli Jan. 22, 1952 2,667,351 McKinney Jan. 26, 1954 2,898,058 Del Mar Aug. 4, 1954 2,770,801 Jones Nov. 13, 1956 2,798,943 lPrideaux July 9, 1957 2,805,065 Cotton Sept. 3, 1957 2,869,120 Lolmaugh et al Jan. 13, 1959 2,879,999 Marshall Mar. 31, 1959 3,010,103 Hopper et al. Nov. 2l, 1961 FOREIGN PATENTS 568,568 Great Britain Apr. 11, 1945 737,318 Great Britain n Sept. 21, 1955 

1. AN AERIAL TOW TARGET COMPRISING A HOLLOW, THINWALLED, RIGID BODY MEMBER HAVING A LOW DRAG AERODYNAMIC CONFIGURATION, A FORWARD END, A TRAILING END, AND A LONGITUDINAL AXIS, THE WALLS OF SAID BODY MEMBER BEING FORMED OF A NON-METALLIC MATERIAL PERMEABLE BY RADAR WAVES; MEANS DEFINING A PLURALITY OF NORMALLY INTERSECTING PLANES ATTACHED TO SAID BODY MEMBER AND POSITIONED INTERIORLY OF SAID BODY MEMBER AND HAVING A METALLIC SURFACE FOR REFLECTING EXTERIORLY PROPAGATED RADAR WAVES; AERODYNAMIC MEANS CARRIED ON SAID BODY MEMBER FOR CONTINUOUSLY ROTATING SAID BODY MEMBER ABOUT ITS LONGITUDINAL AXIS TO STABILIZE SAID BODY MEMBER IN FLIGHT WHEREBY SAID PLURALITY OF INTERSECTING PLANES ARE ROTATED WITH SAID BODY MEMBER TO INCREASE THE PROBABILITY OF DETECTION OF THE TOW TARGET BY THE REFLECTED RADAR WAVES; AN 